The present invention relates generally to combine harvesters and, more particularly, to a rotary cleaning mechanism in combines for cleaning unwanted residue, such as chaff, straw, etc., from threshed grain.
Conventional cleaning systems clean threshed grain by blowing air through a set of planar sieves utilizing gravitational forces to urge cleaned grain through the sieve openings. With the advent of higher capacity threshing and separating mechanisms, such as rotary axial flow combines, the capacity for threshing grain has increased beyond the capacity of conventional cleaning systems to clean the grain. Accordingly, it is desirable to increase both the capacity and the efficiency of cleaning systems in combine harvesters so as not to limit the throughput capability of the combine.
In rotary cleaning mechanisms, as well as in conventional cleaning mechanisms, an efficient flow of air is necessary to provide a proper cleaning action for threshed grain. Since the purpose of a rotary cleaning mechanism utilizing centrifugal forces to urge grain through the cleaning sieve openings is to provide a greater capacity or throughput, a proper air flow to make residue airborne in an efficient manner becomes more critical. Furthermore, it is desirable to provide a blowing fan to positively direct a flow of air that is more concentrated at the forward end of the cleaning cylinder where the mat of grain to be cleaned is thicker. Sucking fans, as is generally found in prior art rotary cleaning devices, will not provide such advantages.